Dinosaurs are fascinating creatures that lived on earth. Their time was far back in history. We cannot find all dinosaur species, but we already know over 700 species of dinosaur species. An article or even a book is not enough to talk about every one of them. Therefore, we need a classification.

Why classification for all dinosaur species?

There are major advantages to the classification of animals. Similarities of different kinds of animals help us to understand the relationship between them. By doing so a large group of animals can be studied as a group. This makes ordinary learning much easier. Besides that, classification preview the diversity of life better and shows us the evolution from simple to complex forms of life.

How to do dinosaurs classification? Well, for any kind of classification you need a system that is based on common characteristics that the subjects you need to classify show. By doing so we can make larger groups and divide them further into smaller groups.

For example, the Tyrannosaurus rex (famous as T-rex) has 3 toes on its foot. It is also a carnivore. So, it belongs to the Saurischian group. Its subgroup will be Theropod because it is a carnivore dinosaur. Just like that very few characteristics are enough to classify a dinosaur.

There are two main groups for all dinosaur species. The pelvis is the main factor in this classification.


Dinosaurs who had their pelvis pubis bone faced backward and down are ornithischians. Other than that, there are other characteristics that ornithischian dinosaurs had in common.

  • All ornithischians were herbivorous.
  • Predentary’ – an extra bone called at the tip of the lower jaw in all ornithischian dinosaurs.
  • Ornithischians had leaf-shaped teeth.

All ornithischians dinosaur species can be divided into five subgroups.


The main factor for a dinosaur to be a thyreophoran is dermal armor. It was made with scale-looking bony plates organized in rows. There were multiple rows parallel to the centerline of the body. Well -developed Supraorbital bone is another characteristic to identify a Thyreophoran.

The most famous thyreophorans were Stegosaurus (the plated dinosaur) and Ankylosaurus (the armored dinosaur). Other than that, Scutellosaurus and Scelidosaurus are good examples of a thyreophoran.


Bony plates, some are small, and some are largely gathered and fit together made an armor that covered their back and flank. They had stout and columnar. Their shin and forearms were shorter than their thighbone and upper arm. Stubby metapodials are another thing they got.

Eupolephalus, Nodosaurus, and Palaceoscincus are prime examples of the Ankylosauria subgroup.


Cerapoda clade is a combination of three groups of Ornithischian dinosaurs. Some of them are bipedal but some are quadrupedal.

  • Ornithopoda
  • Pachycephalosaur
  • Ceratopsia

Marginocephalians group if for all dinosaur species in the last two types above because they share some characteristics like a bony.

Pachycephalosaurs and Ceratopsians are the best examples of Cerapods.


An Ornithischian dinosaur who has a bipedal stance (Like a bird) belongs to the Ornithopoda clade. They lived from the Triassic period to the late cretaceous period (229 million to 65.5 million years ago). We can think of ruminants as the modern equivalent of them. They had developed beaks which they used for crop vegetation.

There are five ornithopod groups

  • Fabrosauridae
  • Heterodontosauridae
  • Hypsilophodontidae
  • Iguanodontidae
  • Hadrosauridae

Heterodontosaurs and Hypilophodon are two examples of ornithopods.


Pachycephalosaurs evolved from Ornithopods, but some say they can be categorized as Ornithopods. The main factor that differentiates them from the rest of the dinosaurs is their unique forehead. It is a marked thickening one. First, we thought it was for the protection but now it is clear that the forehead bone doesn’t give an advantage in a particular situation. They all are bipedal and had leaf-shaped teeth which were very simple. Along their back, there were ossified tendons. They lived in North America in the cretaceous period.

Pachycephalosaurus is large among the clade and Stegoceras is the smallest one. What we know about them is very few. Also, they were rare which makes it even harder to know about them.


The dinosaur pelvis had 3 main bones. Ilium, ischium, and pubis are those. The definition of Saurischia is coming from how these three are placed. For saurischian also known as lizard-hipped pubis points downward and forward at an angle to the ischium.

Birds evolved from one of this group. Now you probably wonder why they are called lizard-hipped, but Ornithischians are bird-hipped. Birds’ hip is placed similar to an Ornithopod even though they evolved from a saurischian their hip is like an Ornithischian.

Another thing that needs to be answered is why fossil records of the Triassic (227 million to 206 million years ago) are better for Saurischians than it for Ornithischians. We still do not know why.

There are two main subgroups of Saurischians. Theropods and Sauropods. They are separated by their choice of food. Two famous dinosaurs of pop culture belong to this.


Theropods are categorized as flesh-eating Saurischian. They lived in the middle Triassic through the Late Cretaceous Epoch (between 245 million and 65.5 million years ago). Throughout the period they were living on every continent except Antarctica.

Therapods were a very diverse group of dinosaurs. Any other group couldn’t beat them in terms of diversity. The smallest theropod was the Microraptor which is the only size of a crow.  The biggest known theropod is Tyrannosaurus rex.

Tyrannosaurus rex is also known as T-rex is the most famous dinosaur. Rex means king in Latin. As the name suggests it was an apex predator of its time. It can reach 27 km/h of maximum speed.


All herbivore Saurischians are sauropods. They are also very popular among us. When we think about dinosaurs other than T-rex, it is sauropods that come into our minds. They have an iconic long neck and long tail body. They were very large. Large enough to recognize as the largest land animals to ever lived on earth. Too close to the largest animals, blue whales.

Sauropods had small heads. Supersaurus is 34m long. It is the longest complete fossil. Even though some other sauropods are assumed to be longer than that, their fossils are incomplete. Argentinosaurus is the prime example with approximately 36m in length. Sauropods were also super tall with sauroposeidon being 18m tall.

All sauropods are quadrupeds. Scientists argue that some of them could stand on two feet. With their long tail touching the ground, doing such a thing could have been possible. They were very massive creatures not to mention their weight is over 80 metric tons.

Sauropods lived in a time were most terrifying creatures roam the earth. Their size was the biggest defense again predators but even then, they might have to fight sometimes. Sauropods lived in age-based herds. They lived for a million years until the extinction of non-avian dinosaurs. So, they are successful species.

That is all dinosaur species with classification. There are plenty of articles about dinosaurs on our website. Check out them and stay with us for more.

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